InnoDB在寫密集的壓力時，由于B-Tree擴展，因而也會帶來數據文件的擴展，然而，InnoDB數據文件擴展需要使用mutex保護數據文件，這就會導致波動。 丁奇的博客說明了這個問題：
When InnoDB under heavy write workload, datafiles will extend quickly, because of B-Tree allocate new pages. But InnoDB need to use mutex to protect datafile, so it will cause performance jitter. Xiaobin Lin said this in his blog:
解決的方法也很簡單，只要知道數據文件可能會增長到多大，預先擴展即可。閱讀代碼可以知道，InnoDB建表后自動初始化大小是FIL_IBD_FILE_INITIAL_SIZE這個常量控制的，而初始化數據文件是由fil_create_new_single_table_tablespace()函數控制的。所以要改變數據文件初始化大小，只要修改fil_create_new_single_table_tablespace的傳入值即可，默認是FIL_IBD_FILE_INITIAL_SIZE。
How to solve it? That's easy. If we know the datafile will extend to which size at most, we can pre-extend it. After reading source code, we can know InnoDB initial datafile size by FIL_IBD_FILE_INITIAL_SIZE, and fil_create_new_single_table_tablespace() function to do it. So if we want to change datafile initial size, we only need to change the initial size parameter in fil_create_new_single_table_tablespace(), the default value is FIL_IBD_FILE_INITIAL_SIZE.
因此，我在建表語法中加上了datafile_initial_size這個參數，例如：
CREATE TABLE test (
…
) ENGINE = InnoDB DATAFILE_INITIAL_SIZE=100000;
如果設定的值比FIL_IBD_FILE_INITIAL_SIZE還小，就依然傳入FIL_IBD_FILE_INITIAL_SIZE給fil_create_new_single_table_tablespace，否則傳入datafile_initial_size進行初始化。
So, I add a new parameter for CREATE TABLE, named ‘datafile_initial_size'. For example:
CREATE TABLE test (
…
) ENGINE = InnoDB DATAFILE_INITIAL_SIZE=100000;
If DATAFILE_INITIAL_SIZE value less than FIL_IBD_FILE_INITIAL_SIZE, I will still pass FIL_IBD_FILE_INITIAL_SIZE to fil_create_new_single_table_tablespace(), otherwise, I pass DATAFILE_INITIAL_SIZE value to fil_create_new_single_table_tablespace() function for initialization.
因此，這個簡單安全的patch就有了，可以看 ?id=67792 關注官方的進展：
So, I wrote this simple patch, see ?id=67792:

復制代碼 代碼如下:

Index: storage/innobase/dict/dict0crea.c
===================================================================
--- storage/innobase/dict/dict0crea.c (revision 3063)
+++ storage/innobase/dict/dict0crea.c (working copy)
@@ -294,7 +294,8 @@
   error = fil_create_new_single_table_tablespace(
    space, path_or_name, is_path,
    flags == DICT_TF_COMPACT ? 0 : flags,
-   FIL_IBD_FILE_INITIAL_SIZE);
+   table->datafile_initial_size < FIL_IBD_FILE_INITIAL_SIZE ?
+        FIL_IBD_FILE_INITIAL_SIZE : table->datafile_initial_size);
   table->space = (unsigned int) space;

   if (error != DB_SUCCESS) {
Index: storage/innobase/handler/ha_innodb.cc
===================================================================
--- storage/innobase/handler/ha_innodb.cc (revision 3063)
+++ storage/innobase/handler/ha_innodb.cc (working copy)
@@ -7155,6 +7155,7 @@
    col_len);
  }

+  table->datafile_initial_size= form->datafile_initial_size;
  error = row_create_table_for_mysql(table, trx);

  if (error == DB_DUPLICATE_KEY) {
@@ -7760,6 +7761,7 @@

  row_mysql_lock_data_dictionary(trx);

+  form->datafile_initial_size= create_info->datafile_initial_size;
  error = create_table_def(trx, form, norm_name,
   create_info->options & HA_LEX_CREATE_TMP_TABLE ? name2 : NULL,
   flags);
Index: storage/innobase/include/dict0mem.h
===================================================================
--- storage/innobase/include/dict0mem.h (revision 3063)
+++ storage/innobase/include/dict0mem.h (working copy)
@@ -678,6 +678,7 @@
 /** Value of dict_table_struct::magic_n */
 # define DICT_TABLE_MAGIC_N 76333786
 #endif /* UNIV_DEBUG */
+  uint datafile_initial_size; /* the initial size of the datafile */
 };

 #ifndef UNIV_NONINL
Index: support-files/mysql.5.5.18.spec
===================================================================
--- support-files/mysql.5.5.18.spec (revision 3063)
+++ support-files/mysql.5.5.18.spec (working copy)
@@ -244,7 +244,7 @@
 Version:        5.5.18
 Release:        %{release}%{?distro_releasetag:.%{distro_releasetag}}
 Distribution:   %{distro_description}
-License:        Copyright (c) 2000, 2011, %{mysql_vendor}. All rights reserved. Under %{license_type} license as shown in the Description field.
+License:        Copyright (c) 2000, 2012, %{mysql_vendor}. All rights reserved. Under %{license_type} license as shown in the Description field.
 Source:         %{src_dir}.tar.gz
 URL:           
 Packager:       MySQL Release Engineering <mysql-build@oss.oracle.com>
Index: sql/table.h
===================================================================
--- sql/table.h (revision 3063)
+++ sql/table.h (working copy)
@@ -596,6 +596,7 @@
   */
   key_map keys_in_use;
   key_map keys_for_keyread;
+  uint datafile_initial_size; /* the initial size of the datafile */
   ha_rows min_rows, max_rows;  /* create information */
   ulong   avg_row_length;  /* create information */
   ulong   version, mysql_version;
@@ -1094,6 +1095,8 @@
 #endif
   MDL_ticket *mdl_ticket;

+  uint datafile_initial_size;
+
   void init(THD *thd, TABLE_LIST *tl);
   bool fill_item_list(List<Item> *item_list) const;
   void reset_item_list(List<Item> *item_list) const;
Index: sql/sql_yacc.yy
===================================================================
--- sql/sql_yacc.yy (revision 3063)
+++ sql/sql_yacc.yy (working copy)
@@ -906,6 +906,7 @@
 %token  DATABASE
 %token  DATABASES
 %token  DATAFILE_SYM
+%token  DATAFILE_INITIAL_SIZE_SYM
 %token  DATA_SYM                      /* SQL-2003-N */
 %token  DATETIME
 %token  DATE_ADD_INTERVAL             /* MYSQL-FUNC */
@@ -5046,6 +5047,18 @@
             Lex->create_info.db_type= $3;
             Lex->create_info.used_fields|= HA_CREATE_USED_ENGINE;
           }
+        | DATAFILE_INITIAL_SIZE_SYM opt_equal ulonglong_num
+          {
+            if ($3 > UINT_MAX32)
+            {
+              Lex->create_info.datafile_initial_size= UINT_MAX32;
+            }
+            else
+            {
+              Lex->create_info.datafile_initial_size= $3;
+            }
+            Lex->create_info.used_fields|= HA_CREATE_USED_DATAFILE_INITIAL_SIZE;
+          }
         | MAX_ROWS opt_equal ulonglong_num
           {
             Lex->create_info.max_rows= $3;
@@ -12585,6 +12598,7 @@
         | CURSOR_NAME_SYM          {}
         | DATA_SYM                 {}
         | DATAFILE_SYM             {}
+        | DATAFILE_INITIAL_SIZE_SYM{}
         | DATETIME                 {}
         | DATE_SYM                 {}
         | DAY_SYM                  {}
Index: sql/handler.h
===================================================================
--- sql/handler.h (revision 3063)
+++ sql/handler.h (working copy)
@@ -387,6 +387,8 @@
 #define HA_CREATE_USED_TRANSACTIONAL    (1L << 20)
 /** Unused. Reserved for future versions. */
 #define HA_CREATE_USED_PAGE_CHECKSUM    (1L << 21)
+/** Used for InnoDB initial table size. */
+#define HA_CREATE_USED_DATAFILE_INITIAL_SIZE (1L << 22)

 typedef ulonglong my_xid; // this line is the same as in log_event.h
 #define MYSQL_XID_PREFIX "MySQLXid"
@@ -1053,6 +1055,7 @@
   LEX_STRING comment;
   const char *data_file_name, *index_file_name;
   const char *alias;
+  uint datafile_initial_size; /* the initial size of the datafile */
   ulonglong max_rows,min_rows;
   ulonglong auto_increment_value;
   ulong table_options;
Index: sql/lex.h
===================================================================
--- sql/lex.h (revision 3063)
+++ sql/lex.h (working copy)
@@ -153,6 +153,7 @@
   { "DATABASE",  SYM(DATABASE)},
   { "DATABASES", SYM(DATABASES)},
   { "DATAFILE",  SYM(DATAFILE_SYM)},
+  { "DATAFILE_INITIAL_SIZE",   SYM(DATAFILE_INITIAL_SIZE_SYM)},
   { "DATE",  SYM(DATE_SYM)},
   { "DATETIME",  SYM(DATETIME)},
   { "DAY",  SYM(DAY_SYM)},